There are several reasons to provide an electrical heating system in a mineral well, particularly in an oil well. Thus, for many petroleum deposits, the liquid sought is relatively viscous but is subject to stimulation for better flow by heating, particularly electrical heating. In other instances, the petroleum may contain constituents that would be solids or near solids at ordinary room temperatures; these constituents include paraffins and asphalts. Petroleum containing substantial quantities of such constituents may flow acceptably at the temperatures encountered in their natural reservoirs, but tend to precipitate as the fluid cools on its way through the well toward the earth's surface. In these circumstances, it may be desirable or necessary to heat some well components, particularly the production tubing through which the petroleum flows to the surface. Of course, it is not unusual for an individual oil well to have characteristics such that both forms of heating are either necessary or desirable.
While electrical heating systems for mineral wells have been proposed that function to accomplish both purposes, such systems have often been relatively inefficient so that electrical heating, either for reservoir stimulation or to preclude precipitation in well operation, is economically unacceptable. In the systems of the present invention, this problem is effectively minimized by appropriate selection of the size, location, and construction of the principal heating electrode employed for reservoir stimulation and of other components employed in the heating system, including particularly electrical and thermal isolation elements. The technique employed to deliver electrical power to the downhole portion of the well where it is particularly needed is also materially improved in many instances, especially for reservoir stimulation.